Dual frequency gregorian-newtonian antenna system with newtonian feed located at common focus of parabolic main dish and ellipsoidal sub-dish



Sept. 27, 1966 BRUNNER DUAL FREQUENCY GREGORIAN-NEWTONIAN ANTENNA SYSTEMWITH NEWTONIAN FEED LOCATED AT COMMON FOCUS OF PARABOLIC MAIN DISH ANDELLIPSOIDAL SUB-DISH Filed May 13, 1964 5 Sheets-Sheet l m Hiv m mw m 2mvmfu 0 T F/ m w W6 2 Y X a E X llm m l E mw v o R|2+ d mm Ex? 3 a m NE3 TO... E AB m G 0 RM 2 F M M O I NA M\ E7 E 0 F F m m f O F 1: I

i D r m I Sept. 27, 1966 J. E. BRUNNER 3,276,022

DUAL FREQUENCY GREGORIAN-NEWTONIAN ANTENNA SYSTEM WITH NEWTONIAN FEEDLOCATED AT COMMON FOCUS OF PARABOLIC MAIN DISH AND ELLIPSOIDAL SUB-DISHFiled May 13, 1964 5 Sheets-Sheet 2 INVENTOR.

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Sept. 27, 1966 J. E. BRUNNER 3,276,022

DUAL FREQUENCY GREGORIAN-NEWTONIAN ANTENNA SYSTEM WITH NEWTONIAN FEEDLCCATED AT COMMON FOCUS OF PARABOLIC MAIN DISH AND ELLIPSOIDAL SUB-DISHFiled May 13, 1964 5 Sheets-Sheet 5 I NVE NTOR.

United States Patent O 3,276,022 DUAL FREQUENCY GREGORIAN-NEWTONIANANTENNA SYSTEM WITH NEWTONIAN FEED LOCATED AT COMMON FOCUS OF PARABOLICMAIN DISH AND ELLIPSOIDAL SUB-DISH John E. Brunner, Hamilton, Ohio,assignor to Aeronca Manufacturing Corporation, Middletown, Ohio, acorporation of Ohio Filed May 13, 1964, Ser. No. 366,965 6 Claims. (Cl.343-727) This invention relates to antenna constructions and isparticularly directed to a novel antenna system effective to operatesimultaneously or sequentially at two widely different frequencies, forexample, at one frequency in the VHF range and another in the UHF or SHFrange.

At the present time it is desirable that antennas for use in fields,such as missile and satellite tracking and telemetering work, operate atany of a number of different frequencies, the higher frequencies beingof an order of more than thirty times the frequencies at the lower endof the range. More particularly, prior to 1960 nearly all mannedaircraft, missile and satellite telemetry and communications wereconducted on a band in the VHF range, i.e., in the 220-260 mc. band.This band is also still used for telemetry from boosters in missilelaunches. At the same time, however, much higher frequencies areutilized in connection with telemetry from newer missiles andsatellites. For example, telemetry and command signals are transmittedin the UHF range from 1500 to 2400 mc., and SHF frequencies from 7200 to10,000 Inc.

The principal object of the present invention is to provide a singleantenna which can be operated at any frequency in the VHF, UHF and SHFbands, and which can in fact be operated simultaneously at two widelydivergent frequencies, for example 220 me. in the VHF band and 8000 me.in the SHF band.

More particularly, the present invention is predicated upon the conceptof providing an antenna system comprising the combination of a singlemain paraboloidal reflector provided with a Newtonian feed at the focusof the paraboloid and an ellipsoidal sub-reflector effective tocooperate with the main reflector and with a second feed at a focus ofthe ellipse to provide a Gregorian antenna unit.

The present antenna system comprises a paraboloidal main reflector andan ellipsoidal sub-reflector disposed so that one focus of theellipsoidal sub-reflector coincides with the focus of the paraboloid.The ellipsoidal reflector is disposed on the side of said common focusremote from the paraboloidal main reflector. A suitable Newtonian VHFfeed, for example a dipole array, is disposed adjacent the common focus.This feed functions in combination with the paraboloidal reflector toprovide the Newtonian unit of the antenna system. In this Newtonian unitthe ellipsoidal sub-reflector serves as a ground plane. The system alsoincludes a second UHF or SH'F feed, for example a feed horn, located atthe second focus of the ellipsoid. The combination of this second feedhorn, the ellipsoidal reflector and paraboloidal reflector function asthe Gregorian unit of the antenna system.

-The present invention is predicated in part upon the empiricaldiscovery and determination that the elements of the two systems arecompatible, i.e. the elements nec essary for one system do not adverselyaifect the operation of the other system to an objectionable degree.Specifically, it has been found that the operation of the Gregorianportion of the antenna system is only minimally aflected by the presenceof the dipole array in front of the ellipsoidal reflector. Similarly,the adverse affects on the operation of the Newtonian portion of thesystem due to the use of an ellipsoidal ground plane rather than theideal planar ground plane are well within tolerable limits.

One important advantage of the present antenna system is that it can beoperated simultaneously at two widely divergent frequencies. Moreover,the present antenna can be operated sequentially at widely differentfrequencies without any need for physically modifying the antenna tochange from one frequency to another.

Another important advantage of the present antenna system ish that itprovides two different types of antennas, each type being effective toprovide. optimum efficiency for signals in a particular frequency range.Specifically, in the VHF frequency range the ray-optical performance ofa double reflector system, such as a Gregorian system, deterioratesrapidly because the physical size of the sub-reflector is no longerlarge with respect to the wave length. Also, gain loss and side lobedegradation render the use of an antenna system of this type impracticalin this frequency range. In accordance with the present invention, thedouble reflector system is not utilized in this range, but rather aNewtonian feed is provided with the result that optimum antennaperformance is achieved in the VHF range.

At the same time, in the UHF and SHF range, the Gregorian doublereflector system is utilized. The system provides many advantagesleading to optimum performance in these ranges including low spill over,reduced space attenuation and convenient location of the primary feedadjacent to the paraboloid vertex.

Another very important advantage of the present antenna system is thatit utilizes a single main paraboloidal reflector surface. This isparticularly important since it facilitates the construction of a largeantenna, for example an antenna 60 in diameter, a size which would notbe practical if it were necessary to provide two main paraboloidalreflectors.

Still another advantage of the present invention is that both the mainparaboloidal reflector and the ellipsoidal sub-reflector are providedwith conventional reflector surfaces, i.e. neither of these surfaces isrequired to be selectively reflective of one radiation frequency and/orpolarization and transmittive of the other.

A further advantage of the present invention is that the axis of boththe Newtonian antenna unit and the Gregorian antenna unit arecoincident, with both feeds lying substantially on the common axis. Thissimplifies positioning of the antenna and handling of the antennasignals.

illustrating a preferred embodiment of the invention.

In the drawings:

FIGURE 1 is a perspective view of one antenna system constructed inaccordance with the present invention.

FIGURE 2 is a diagrammatic view showing the geometric relationship ofthe components of the system.

FIGURE 3 is a diagrammatic view showing the parameters of theellipsoidal reflector.

FIGURE 4 is a diagrammatic view showing the ray geometry of theNewtonian feed portion :of the antenna system.

FIGURE 5 is a diagrammatic view showing the ray geometry of theGregorian portion of the antenna system.

FIGURE 6 is a front elevational view of the ellipsoidal reflector andthe dipole array for providing the Newtonian feed.

FIGURE 7 is an enlarged view taken generally along line 77 of FIGURE 1.

One prefer-red form of antenna system 10 constructed 'in accordance withthe principles of the present inven- 3 tion comprises a paraboloidalmain reflector 11 carried by a frame structure 12. The frame 12 is inturn connected to a drive unit 13 which is effective to shift theantenna both in azimuth and elevation. It is to be understood that theframe and antenna drive are conventional and constitute no part of thepresent invention. In fact, the present antenna can be mounted upon astationary support, if desired, in a particular installation.

In addition to the main paraboloidal reflector member 11, the presentantenna system comprises a secondary ellipsoidal reflector member 14mounted in front of main reflector 11, as by means of support beams 15.The antenna system further comprises a Newtonian feed, such as dipolearray 17, carried by the ellipsoidal reflector member 14 and located atthe focus of the paraboloidal reflector. A second, or Gregorian, feedmember such as horn 18 extends through an opening in the vertex of theparabola and is directed toward the ellipsoidal reflector.

The exact geometry and manner of functioning of the antenna systemcomponents is shown diagrammatically in FIGURES 2-4. More particularly,the front face 11' of reflector 11 is a continuous reflective paraboloidsurface formed of a conductive metal, such as aluminum. This surface isgenerated by rotating a generating parabola 11a about axis 20. As isshown in FIGURE 2, the generating parabola 11a has a focal point F whichalso corresponds to the focal point of the paraboloidal reflectorsurface 11. The focal length of the parabola is designated fin and thelocus of the generating parabola in the Cartesian system shown in FIGURE2 with the origin is Y =4fmX The paraboloidal reflector has a maximumdiameter designated D. I have empirically determined that in the presentantenna system it is preferable to utilize a paraboloid having arelatively small fm/D ratio, for example a ratio of the order of .30.For larger ratios, the ellipsoidal sub-reflector member 14 must beplaced an excessive distance from the paraboloidal reflector. Thisgreatly increases the difficulties involved in rigidly mounting theellipsoidal reflector relative to the paraboloidal reflector and alsothe larger support beams required adversely affect operation of theantenna.

One suitable form of ellipsoidal reflector 14 is machined from a solidaluminum or other conductive metal member. The actual reflector surface21 of this member is of ellipsoid configuration and is obtained byrotating generating ellipse 21a about its major axis, i.e. the axisthrough its focii. In the present antenna system, one focus of theellipse is common with the focus F of the parabola and the major axis ofthe ellipse iscoincident with axis 20 of the paraboloid. Consequently,the second focus of the ellipse 0 also lies on axis 20. In the presentembodiment, this second focal point lies in front of the face of theparaboloidal reflector, i.e. between the paraboloidal reflector andellipsoidal reflector. It is to be understood, however, that theconfiguration of the paraboloidal reflector and ellipsoidal reflectorcould be such that the second focal point falls behind the paraboloidalreflector if desired.

One vertex 22 of the generating ellipse is spaced a distance M beyondthe focal point F The distance between the focii O and F of the ellipseis indicated by the letter F. The center of the ellipse, i.e. the midpoint between 0 and F is designated 0 The semi major axis of the ellipseis designated by the letter a and the semi minor axis is indicated bythe letter 12. In terms of a Cartesian coordinate system having theabcissa axis coincident with axis 20 and the ordinate axis passingthrough the center of ellipse 0 the locus of the'ellipse is defined bythe equation X /a +Y /b =l.

FIGURES 4 and are diagrammatic views corresponding to the verticalsections through the antenna system along axis 20. (FIGURE 2 can also beconsidered as corresponding to these views.) FIGURE 4 shows the .areequal.

initial orbit.

ray. geometry of the Newtonian unit of the antenna system. Moreparticularly, the Newtonian feed comprises dipole array 17, the detailsof which are explained below. Essentially, however, this dipole arrayhas a feed phase center substantially coincident with the parabola focusF,,. In connection with the Newtonian feed, ellipsoidal reflector 21functions as a ground plane for the dipoles. The spherical phase frontemitted by the feed is collimated or converted to plane phase fronts bythe paraboloidal reflector surface 11' in the manner shown in FIGURE 4.Thus, dipole array 17 provides conventional Newtonian feed for parabolicreflector 11.

FIGURE 5 shows the geometry of the Gregorian unit of the antenna system.As there shown, a suitable UHF or SHF feed, such as diagonal horn 18, ismounted coaxially with paraboloidal axis 20 at the seco'nd'focal point 0of the ellipse. Radiation from the feed horn strikes the ellipse and isreflected from the ellipse onto the parabola and collimated in themanner shown in FIGURE 5. 1 Specifically, in order to collimate energyfrom the feed born 18 into a beam, the length of all rays from the focalpoint 0 to a reference plane QQ must be equal (assuming constant phasevelocity for all paths). The ellipsoidal reflector has the property thatthe lengths of all rays from one focusO to a point on the ellipse andback to the other focus F are equal. Similarly, the paraboloidalreflector has the property that the lengths of all rays from the focalpoint F to the reference plane QQ Thus, since the focal point F of theparaboloidal reflector and the second focus F of the ellipsoidalreflector coincide and the horn 18 is located at the second focal point0 of the ellipse,,the necessary conditions are present and the rays fromthe horn are in fact collimated.

The physical construction of horn 18 is conventional as is the manner ofconnecting a VHF or UHF transmitter or receiver to the horn.Accordingly, it is not considered necessary to describe the details ofconstruction of this horn member and its connections in the presentapplication.

The details of the dipole array 17 are best shown in FIGURES 6 and 7. Asthere shown, the dip-ole array 17 comprises an array of four slotbalun-feed one-half Wave dipoles 24 with a length to diameter ratio often to one. The dipoles 24 are connected in a conventional manner forsum and dilference node feeding via four ra-trace type hybrids. As isshown in FIGURE 6, the Wings 25 of the dipoles are arrangedsymmetricallyrelative toparaboloid axis 20. The dipoles are also spaceda slight distance on the side of focal point F remote from ellipsoidalreflector surface 21. As a result, the dipole feed sum mode phase centercoincides substantially with the focal point F of the paraboloidalreflector. Connections to the dipole wings 25 are made throughfeed-lines 27 which pass rearwardly through openings formed in reflectormember 14.

ftonian unit is used to track the booster during the initial stage of amissile launch. Conventionally, a booster transmits signals in the VHFband, i.e. of the order of 220 me. When the booster and missile passover the horizon, the Gregorian feed is energized and the antennadirected by drive 13 toward the position in which the satellite isexpected to appear at the conclusion of its Telemetry signals from thesatellite are usually transmitted on the UHF or SHF band, for example ata frequency of the order of 8000 me. These signals are efl'icientlyreceived by the Gregorian unit of the system. It will also beappreciated that the Newtonian and Gregorian units could 'be usedsimultaneously if desired. Also, the antenna can 'be utilized totransmit command signals in the VHF range using'the Newtonian feed andin the UHF or SHF ranges utilizing the Gregorian feed.

From the foregoing disclosure of the general principles of the presentinvention and the above description of a preferred embodiment, thoseskilled in the art will readily appreciate various modifications towhich the invention is susceptible. For example, it is contemplated thatthe present antenna system can be utilized at still other frequencyranges than those described, e.g. in the infrared range. In any case,however, the diameter of the ellipsoidal sub-reflector must be largewith respect to the wave length of the Gregorian feed, i.e. greater than8x, so that substantially ray-optic performance is realized in theGregorian unit as well as in the Newtonian unit of the antenna. It isfurther contemplated that other elements than the specific dipole arrayand horn members described can be employed to form the Newtonian andGregorian feeds. Therefore, I desire to be limited only by the scope ofthe following claims.

Having described my invention, I claim:

1. An antenna system for simultaneously operating at two frequencies,said antenna system comprising a single paraboloidal main reflectorhaving an axis and a focus located on said axis, an elliposidalsub-reflector having a continuous surface and having one focuscoincident with said paraboloidal focus and having a second focuslocated on said axis, a first feed means directed toward saidparaboloidal reflector, said first feed means being disposed at thefocus of said paraboloidal reflector to provide a Newtonian feed, secondfeed means disposed on said axis at the second focus of said ellipsoidfor providing a Gregorian feed, said second Gregorian feed meansoperating at a substantially higher frequency than said first Newtonianfeed, said antenna being effective to reflect both said Gregorian feedand said Newtonian feed with substantially optic-ray performance.

2. An antenna system for simultaneously operating at two frequencies,said antenna system comprising a single paraboloidal main reflectorhaving an axis and a focus located on said axis, an ellipsoidalsub-reflector having a continuous surface and having one focuscoincident with said paraboloidal focus and having a second focuslocated on said axis, a dipole array carried by said ellipsoidalsub-reflector intermediate said ellipsoidal sub-reflector and saidparaboloidal reflector, said dipole array hav ing a plurality of spaceddipoles having a feed phase center disposed substantially at the focusof said paraboloidal reflector to provide a Newtonian feed, and secondfeed means disposed on said axis at the second focus of said ellipsoidfor providing a Gregorian feed.

3. An antenna system for simultaneously operating at .two frequencies,said antenna system comprising a single paraboloidal main reflectorhaving an axis and a focus located on said axis, an ellipsoidalsub-reflector having a continuous surface and having one focuscoincident with said paraboloidal focus and having a second focuslocated on said axis, a dipole array carried by said ellipsoidalsub-reflector intermediate said ellipsoidal sub-reflector and saidparaboloidal reflector, said dipole array having a plurality of spaceddipoles having a feed phase center disposed substantially at the focusof said paraboloidal reflector to provide a Newtonian feed, saidellipsoidal subreflector functioning as a ground plane for said dipolearray, and second feed means disposed on said axis at the second focusof said ellipsoid for providing a Gregorian feed.

4. An antenna system for simultaneously operating at two frequencies,said antenna system comprising a single paraboloidal main reflectorhaving an axis and a focus located on said axis, an ellipsoidalsub-reflector having a continuous surface and having one focuscoincident with said paraboloidal focus and having a second focuslocated on said axis, a dipole array carried by said ellipsoidalsub-reflector intermediate said ellipsoidal sub-reflector and saidparaboloidal reflector, said dipole array having a plurality of spaceddipoles having a feed phase center disposed substantially at the focusof said paraboloidal reflector to provide a Newtonian feed, and adiagonal feed horn extending through an opening in the vertex of saidparaboloidal main reflector, said diagonal feed horn being disposed onsaid axis at the second focus of said ellipsoid for providing aGregorian feed.

5. An antenna system for simultaneously operating at .two frequencies,said antenna system comprising a single paraboloidal main reflectorhaving an axis and a focus located on said axis, said paraboloidal mainreflector having an f/D ratio of the order of .30, an ellipsoidalsubreflector having a continuous surface and having one focus coincidentwith said paraboloidal focus and having a second focus located on saidaxis, a first feed means directed toward said paraboloidal reflector,said first feed means being disposed at the focus of said paraboloidalreflector to provide a Newtonian feed, second feed means disposed onsaid axis at the second focus of said ellipsoid for providing aGregorian feed.

6. An antenna system for simultaneously operating at two frequencies,said antenna system comprising a single paraboloidal main reflectorhaving an axis and a focus located on said axis, an ellipsoidalsub-reflector having a continuous surface and having one focuscoincident with said paraboloidal focus and having a second focuslocated on said axis, a first feed means directed toward saidparaboloidal reflector, said first feed means being disposed at thefocus of said paraboloidal reflector .to provide a Newtonian feed,second feed means disposed on said axis at the second focus of saidellipsoid for providing a Gregorian feed, said second Gregorian feedmeans operating at a substantially higher frequency than said firstNewtonian feed, said antenna being effective to reflect both saidGregorian feed and said Newtonian feed with substantially optic-rayperformance, irrespective of the polarization of the feeds.

References Cited by the Examiner UNITED STATES PATENTS 2,540,518 2/1961Gluyas 343-837 2,972,743 2/1961 Svensson et a1 343-781 3,148,370 9/1964Bowman 343781 HERMAN KARL SAALBACH, Primary Examiner. R. F. HUNT, JR.,Assistant Examiner.

1. AN ANTENNA SYSTEM FOR SIMULTANEOUSLY OPERATING AT TWO FREQUENCIES,SAID ANTENNA SYSTEM COMPRISING A SINGLE PARABOLOIDAL MAIN REFLECTORHAVING AN AXIS AND A FOCUS LOCATED ON SAID AXIS, AN ALLIPOSIDALSUB-REFLECTOR HAVING A CONTINUOUS SURFACE AND HAVING ONE FOCUSCOINCIDENT WITH SAID PARABOLOIDAL FOCUS AND HAVING A SECOND FOCUSLOCATED ON SAID AXIS, A FIRST FEED MEANS DIRECTED TOWARD SAIDPARABOLOIDAL REFLECTOR, SAID FIRST FEED MEANS BEING DISPOSED AT THEFOCUS OF SAID PARABOLOIDAL REFLECTOR TO PROVIDE A NEWTONIAN FEED, SECONDFEED MEANS DISPOSED ON SAID AXIS AT THE SECOND FOCUS OF SAID ELLIPSOIDFOR PROVIDING A GREGORIAN FEED, SAID SECOND GREGORIAN FEED MEANSOPERATING AT A SUBSTANTIALLY HIGHER FREQUENCY THAN SAID FIRST NEWTONIANFEED, SAID ANTENNA BEING EFFECTIVE TO REFLECT BOTH SAID GREGORIAN FEEDAND SAID NEWTONIAN FEED WITH SUBSTANTIALLY OPTIC-RAY PERFORMANCE.